Belt

ABSTRACT

A belt assembly is provided for use as an endless belt traveling relative to a frame structure. The belt assembly comprises a first fabric layer and a second fabric layer having an outer surface that at least partially forms a bottom surface of the belt. A composition comprising polyvinyl chloride is adhered to the inner surface of the first fabric layer. A composition comprising polyurethane is adhered to the inner surface of the second fabric layer. A coating composition comprising polyvinyl chloride is disposed between the inner surfaces of the first fabric layer and the second fabric layer for joining the first fabric layer and the second fabric layer. An at least substantially solid lubricant composition is impregnated in the second fabric layer and at least partially forms the bottom surface of the belt.

CROSS-REFERENCES

Some of the material disclosed and claimed in this application is alsodisclosed in U.S. patent application Ser. No. 10/337,646, filed Jan. 7,2003, entitled “Treadmill Belt”, and U.S. patent application Ser. No.10/337,706, filed Jan. 7, 2003, entitled “Treadmill Belt”. The contentsof the above patent applications are incorporated herein by reference intheir entirety. Both of the above-referenced applications are currentlypending.

BACKGROUND

This invention relates generally to a belt, and more particularly to alubricated belt for use in applications such as conveying systems.

Conveying systems are used in a number of applications, particularlymaterial handling, package handling and sortation, and the like. Onesuch application is baggage conveying systems in airports.

A conveying system generally comprises an endless belt having a top, orouter, surface and a bottom, or inner, surface; guide rollers aroundwhich the belt passes; and spaced support rollers for supporting thebelt. The belt is driven, directly or indirectly, by a motor so that thebottom surface of the belt slides across the rollers. In some conveyingsystems, such as systems for airport baggage handling, the supportrollers are replaced by a stationary slider bed, or deck, for supportingthe belt. The bottom surface of the belt slides across the upper surfaceof the slider bed, which is typically formed from steel or other rigidmaterial.

An endless belt may be made by joining opposite ends of a belt material.Belts are often given a one or two-sided coating to provide certaindesirable characteristics to the belt. Accordingly, different materialswith different characteristics may be used for the coating. For example,various thermoplastic materials, such as PVC or polyurethane, are usedfor coating a belt for use in conveying systems.

The action of the belt passing over the rollers or across the slider bedgenerates friction between the bottom surface of the belt and thesurfaces of the rollers or the slider bed. Efforts have been made toreduce this friction in order to reduce the power consumption requiredto drive the belt, friction-induced heating, and friction-induced noise.Reducing the friction can also enhance the operational life of the belt.It is known to reduce the friction of a belt through the use oflubrication on the bottom surface of the belt, and there are severalknown lubricants and associated methods. The underlying construction ofthe belt can also affect the resulting friction.

In addition, belts for use in certain applications must meet defineddurability and flammability criteria. For example, a belt for use in anairport baggage conveyor system must be puncture and tear resistant andnon-flammable. The defined criteria and test methods for belts in theU.S. are specified in ASTM D 378, “Standard Test Methods For Rubber(Elastomeric) Belting, Flat Type”, which covers the procedures forevaluating the physical properties of flat conveyor belting, includingflammability. Meeting the flammability requirement of ASTM D 378necessitates applying a flame retardant coating to the belt. However, ithas been found that the non-flammable coating can prevent absorption oflubricant coatings.

For the foregoing reasons, there is a need for a belt with a reducedcoefficient of friction for use, for example, in a conveyor system. Thenew belt should be able to meet desired criteria for operability andfunctionality in a preferred application.

SUMMARY

Accordingly, as described herein, a belt assembly is provided for use asan endless belt traveling relative to a frame structure. The beltassembly comprises a first fabric layer having an inner surface and anouter surface that at least partially forms an upper surface of thebelt. A composition comprising polyvinyl chloride is adhered to theinner surface of the first fabric layer such that the coatingcomposition at least partially forms the inner surface of the firstfabric layer. A second fabric layer has an inner surface and an outersurface that at least partially forms a bottom surface of the belt. Acomposition comprising polyurethane is adhered to the inner surface ofthe second fabric layer such that the coating composition at leastpartially forms the inner surface of the second fabric layer. A coatingcomposition comprising polyvinyl chloride is disposed between the innersurface of the first fabric layer and the inner surface of the secondfabric layer for joining the first fabric layer and the second fabriclayer. An at least substantially solid lubricant composition isimpregnated in the second fabric layer and at least partially forms thebottom surface of the belt.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, referenceshould now be had to the embodiments shown in the accompanying drawingsand described below. In the drawings:

FIG. 1 is a schematic, side elevational view of a portion of anembodiment of a conveyor system for use with a belt according to anembodiment of the present invention.

FIG. 2 is a schematic, elevational, partial view of a longitudinallyextending portion of an upper run of a belt according to an embodimentof the present invention; and

FIG. 3 diagrammatically illustrates a method and apparatus for formingan endless belt from a roll of belt material according to the presentinvention.

DESCRIPTION

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the invention. For example, words such as“upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,”and “downward” merely describe the configuration shown in the FIGs.Indeed, the components may be oriented in any direction and theterminology, therefore, should be understood as encompassing suchvariations unless specified otherwise.

Referring now to the drawings, wherein like reference numerals designatecorresponding or similar elements throughout the several views, FIG. 1is a schematic side elevational view of a portion of a conveying systemgenerally designated at 10. The conveying system 10 includes an endlessbelt 12 that passes around a pair of guide rollers 14 rotatably mountedat each end of a frame 16 for carrying the belt 12. The belt 12 isendless by virtue of opposite ends of the belt being joined together ata joint, which is preferably in the form of a splice (not shown). Thebelt 12 is typically substantially uniform along its length except forat the joint. The belt 12 can be a variety of different lengths and canalso be a variety of different widths, which is the distance betweenside edges of the belt 12. The length of the belt 12 is preferably manytimes greater than the width.

As shown in FIG. 1, the belt 12 extends around the rollers 14 so thatthe bottom surface of the upper run of the belt engages a slider bed 15,and the upper surface of the upper run of the belt faces away from theslider bed 15. The upper surface of the belt 12 is shown carryingbaggage 22, or the like, which contributes to the friction resultingfrom the bottom surface of the belt 12 sliding across the slider bed 15.One of the guide rollers 14 is driven, such as via a drive belt 18, by amotor 20 that is mounted to the frame 16. The direction of movement ofthe belt 12 is denoted by the arrows. It is understood that a variety ofother types of mechanisms for driving the belt 12 are also within thescope of the present invention.

Referring now to FIG. 2, there is shown a schematic partial view of alongitudinally extending portion of the upper run of the belt 12according to the present invention. The belt 12 includes a top ply 24and a bottom ply 26 joined by an intermediate layer 30 therebetween. Theupper surface of the top ply 24 is substantially planar and is definedby a flame retardant polyvinyl chloride (PVC) coating 25 that is adheredto and covers the top ply 24. The top ply 24 may further comprise afriction surface for moving objects on an incline.

The bottom ply 26 includes a bottom surface 27 which slides across theslider bed 15 and around the guide rollers 14 (FIG. 1). The bottomsurface 27 is preferably substantially planar, except for the texture ofthe fabric of the bottom ply 26 and any discontinuity in the region ofthe joint. As will be more fully described herein, the construction ofthe bottom ply 26 provides a low coefficient of friction as against theguide rollers 14 and the slider bed 15.

The intermediate layer 30 is disposed between and joins the top ply 24and the bottom ply 26. The intermediate layer comprises a flameretardant PVC adhesive coating 32 adhered to the inner surface of thetop ply 24. A polyurethane adhesive coating 34 is adhered to the innersurface of the bottom ply 26. A middle layer comprising a flameretardant PVC layer 36 is disposed between the two adhesive coatings 32,34. The middle layer PVC coating 36 is about 0.5 mm thick and functionsto separate the top ply 24 and the bottom ply 26 and further provideslateral stiffness and puncture and tear resistance to the belt 12construction.

According to the present invention, the belt 12 includes a lubricantcoating composition 40 that is impregnated in the bottom ply 26 and isproximate the bottom surface 27 of the bottom ply 26. In FIG. 2, thelubricant coating composition 40 is schematically illustrated bystippling (i.e., dots and flicks) in the bottom ply 26.

FIG. 3 diagrammatically illustrates a method and apparatus for formingan endless belt 12 according to an embodiment of the present invention.A roll 44 of belt material 46 is provided, for example, a wovenpolyester fabric for forming the top ply 24. The belt material 46 isunwound from the roll 44 by one or more transport mechanisms 48 arrangedalong the travel path of the belt material 46.

The belt material 46 is initially passed through a coater 50. Any typeof suitable coater known in the art of wide web or textile coating maybe used. Exemplary coaters include knife coaters, roll coaters, and thelike. In the coater 50, a liquid PVC plastisol primer 25 is applied to(e.g., poured onto, or the like) the upper surface of the fabric of thetop ply 24 of the belt material 46. The PVC plastisol primer 25 alsocontains a flame retardant such as antimony trioxide and aluminumtrihydrate, although other suitable flame retardants are availableincluding phosphoric acid ester plasticizer, brominated flame retardantand the like, and an isocyanate bonding agent. The purpose of the PVCplastisol primer 25 is to protect the polyester fabric from burning, andalso to act as an adhesive layer for a second, cover coating which maybe applied later. In some cases, the PVC plastisol primer 25 alsocontains pigment and acts as the carrying surface of the finished belt.More particularly, the PVC plastisol primer 25 is applied at a positionjust upstream from a nip defined between an upper knife edge and a lowerroller. The liquid of the coating composition is forced into the fabricof the top ply 24 of the belt material 46 as it passes through the nip.

Thereafter, the belt material 46 with the liquid PVC plastisol primer iscured by transporting the belt material through a drying oven 52suspended in a tenter frame, or the like. The belt material 46 is thentransported through a cooling mechanism 54, where the now coated beltmaterial 56 is cooled, such as by nipping the coated belt materialbetween chilled rollers. The coated belt material 56 is then formed intoa roll 57.

Next the fabric of the top ply 24 receives the same PVC plastisol primer32 on the bottom, or inner, surface. The purpose of this coating of PVCplastisol primer 32 is, again, to protect the polyester fabric fromburning and to act as an adhesive layer between the top ply 24 fabricand the intermediate layer 30. The method of applying the second coatingof PVC plastisol primer 32 is the same as described above, beginningwith the roll of belt material 44. However, in this pass through theapparatus, the belt material 46 is of course already coated on one sidewith the PVC plastisol primer 25.

A second roll 44 of belt material 46, for example, woven polyesterfabric, is provided for forming the bottom ply 26. The belt material 46is unwound from the roll 44 by the one or more transport mechanisms 48and passed through the coater 50. In the coater 50, a liquid,solvent-based polyurethane primer 34 is applied to the top, or inner,surface of the fabric of the bottom ply 26 of the belt material 46. Thepolyurethane primer 34 acts as an adhesive layer between the bottom ply26 and the intermediate layer 30. A flame retardant additive to thepolyurethane primer 34 is optional. Thereafter, the belt material 46 ofthe bottom ply 26 is cured by transporting through the drying oven 52suspended in a tenter frame, or the like. The belt material 46 of thebottom ply 26 is then transported through the cooling mechanism 54,where the now coated belt material 56 is cooled, such as by nipping thecoated belt material between chilled rollers. The coated belt material56 is then formed into a roll 57.

Next, the coated top ply 24 and the coated bottom ply 26 are laminatedtogether using a PVC plastisol 36 including a flame retardant. Theliquid PVC plastisol 36 is applied to the primer-coated inner surface ofeither the top ply 24 or the bottom ply 26. The other of the top ply 24or the bottom ply 26 is then nipped onto the coated fabric ply andpassed through the drying oven 52 to cure and solidify the PVC plastisol36 layer thus forming, for example, a two-ply belt. The polyurethanecoating 34 on the inner surface of the bottom ply 26 serves as a barriercoating, preventing significant penetration or absorption of the PVCplastisols 32, 36 of the intermediate layer 30 into the bottom ply 26.This allows the fabric of the bottom ply 26 to remain “open” so that alubricant coating composition 40 applied to the bottom surface 27 of thebottom ply 26 can substantially fill the interstices between the fibersof the fabric.

Following the lamination step, the belt 12 is run upside down throughthe apparatus, such that the bottom surface 27 of the bottom ply 26 ofthe belt 12 is facing upward, since this surface will eventually contactthe slider bed 15 and guide rollers 14. In the coater 50, a liquidlubricant composition 40 is applied to the bottom surface 27 of thebottom ply 26 at a position just upstream from the nip so that theliquid lubricant composition 40 is forced into the fabric of the bottomply 26 as it passes through the nip. The belt with the liquid lubricantcomposition is cured by transporting through the drying oven 52suspended in the tenter frame, or the like.

The oven curing of the lubricant coating dries any solvent or water, andalso melts the solid component of the lubricant composition 40 allowingthe lubricant to flow into the spaces in the fabric of the bottom ply26. Volatilization of the solvent component of the lubricant composition40 in the drying oven 52 results in an at least substantially solidlubricant coating 40 being impregnated in the bottom ply 26 of the belt12.

The dwell time for each incremental portion of the belt 12 within thedrying oven 52 is about 1 to 5 minutes, or more specifically about 2minutes, and the temperature within the oven is about 80° to 200° C., ormore specifically about 100° C.

The belt 12 is then transported through the cooling mechanism 54 andformed into a roll 57. Thereafter, and in some cases at a differentfacility, the coated belt material 56 is unwound from the roll 57 by oneor more transport mechanisms 58 positioned along the travel path of thebelt. At a cutting mechanism 60, sections of the belt material 62 arecut from the coated belt material 56. At a splicing mechanism 64, eachof the sections of belt material 62 is joined end-to-end to form anendless belt, as is known in the art. Most of the joints, or splices, inbelts used in airport baggage conveying systems will be metal lacing.The splice may extend at an oblique angle relative to the longitudinallyextending edges of the belt 12. The belt 12 is preferably substantiallyuniform along its length except for in the region of the splice.

It is understood that the process described above is merely exemplaryand that a different sequence or additional process steps may be usedduring the manufacture of an endless belt according to the presentinvention. For example, additional coatings of PVC, or other polymer,can be applied over the PVC primer coating 25 on the upper surface ofthe top ply 24 in order to act as a carrying surface. Variousproperties, such as high friction coefficient, abrasion resistance, ortexture can be imparted into this top coating, depending on the specificfunction of the belt 12. For example, a soft PVC coating withlongitudinal grooves might be used for incline conveyors, in order tohave a sufficiently high friction coefficient to elevate goods withoutslippage relative to the top surface. Further, it is possible to useother materials than those described above. For example, fabric madefrom other fibers such as nylon, aramide, cotton or other materialscould be used, and the coatings could be made from polyurethane,polyethylene, silicone rubber, or other suitable materials.

As described above, the belt 12 according to the present inventionincludes three main layers: the top ply 24, the bottom ply 26, and anintermediate layer 30. The top ply 24 is preferably a plainly wovenfabric. The top ply 24 may be formed of any woven fabric exhibitingsufficient durability and flexibility for an intended application. Forairport baggage handling, for example, the top ply fabric is designed tobe tear and puncture resistant. In one embodiment woven fabric formedfrom polyester yarns, particularly multifilament polyester yarns havinga denier of about 1000, is suitable. As used herein, the term “yarn”refers to any continuous strand of textile fibers, filaments or materialin a form suitable for knitting, weaving, or otherwise intertwining toform a textile fabric. In accordance with one embodiment of the presentinvention, all of the fabrics of the belt 12 are constructed solely ofman-made filaments or fibers, although natural fibers may be used inalternative embodiments. In one embodiment, the fabric construction ofthe top ply 24 is a plain weave, including is thirty-four (34) 2,000denier polyester multifilament warp yarns per inch of belt width and25.4 0.4 mm diameter polyester monofilament weft yarns per inch of beltlength. This fabric construction provides a laterally stiff belt withhigh tear and puncture resistance.

The bottom ply 26 may be formed from any fabric providing sufficientstrength, durability and frictional properties to the resulting belt 12construction. According to one embodiment of the present invention, thefabric of the bottom ply 26 includes an effective amount of relativelyfine or low twist warp yarns. As used herein, the term “warp yarn”refers to those yarns within a given layer which extend in thelongitudinal direction, that is, along the length of the belt 12.Correspondingly, as used herein, the term “weft yarns” refers to thoseyarns within a given layer that extend in a transverse direction, thatis, across the belt 12. Although not wishing to be bound by theory,theoretically the incorporation of relatively fine or low twist warpyarn into the bottom ply 26 decreases the coefficient of frictionbetween the bottom surface 27 of the belt 12 and the slider bed 15 (FIG.1).

Accordingly, an effective amount of the warp yarns within the bottom ply26 preferably have a relatively fine denier, such as a denier of lessthan about 1000, and, more preferably, a denier of about 500 or smaller.As an additional example, an effective amount of the warp yarns withinthe bottom ply 26 have a denier ranging from about 150 to 500. Accordingto one embodiment of the present invention, 100% of the warp yarns ofthe fabric of the bottom ply 26 are the relatively fine denier yarn.

The warp yarns of the bottom ply 26 may possess low twist, such as atwist of less than about 2.5 complete turns per inch, and mostpreferably twist ranging from about 1.5 to 2.0 complete turns per inch.Regarding the warp yarns of the bottom ply 26, a twist of about 2.0complete turns per inch may be most preferred for facilitating weaving,whereas a twist of about 1.5 complete turns per inch may be mostpreferred for reducing the friction generated between the bottom ply 26and the slider bed (FIG. 1).

According to the present invention, the bottom ply 26 warp yarnspreferably are formed from polyethylene terephthalate, they are about500 denier or smaller, and each is twisted about 1.5 to 2.0 completeturns per inch. The bottom ply 26 weft yarns are preferably formed frompolyester monofilament fiber, and the monofilament weft yarns eachpreferably have a diameter of about 0.2 mm. The fabric of the bottom ply26 is preferably a 2/1 twill weave, wherein the warp yarn preferablypasses under two weft yarns for every weft yarn it passes over, so thatthe long, floating portions of the warp yarns contact the slider bed 15(FIG. 1) that the belt slides across, with the belt traveling in thedirection in which the warp yarns extend. The bottom ply 136 fabric has45×50 yarns per inch (i.e., 45 warp ends per inch and 50 weft ends perinch). One exemplary commercially available fabric for use in the bottomply 26 is Style Code No. 5523, produced by Milliken & Company ofSpartanburg, S.C.

As mentioned above, the relatively fine size or the low twist of thewarp yarns in the bottom ply 26 are believed to reduce friction betweenthe bottom surface 27 of the belt 12 and the slider bed 15 (FIG. 1).According to the present invention, the coefficient of friction betweenthe bottom surface 27 of the belt 12 and the slider bed is preferablyfurther reduced by an at least substantially solid lubricant composition40 that is impregnated in the fabric of the bottom ply 26 and isproximate the bottom surface 27. As used herein, the term “solid” meansthat the solvents employed within the corresponding liquid lubricantcomposition, from which the solid lubricant composition 40 has beenformed, have been substantially removed, such as by volatization and thelike. The solid lubricant composition 40 is preferably a mixture, andmost preferably is a substantially uniformly dispersed mixture. In FIG.2, the solid lubricant composition 40 is schematically illustrated bystippling (i.e., dots and flicks) in the bottom ply 26.

The solid lubricant composition 40 preferably includes one or morehigher viscosity lubricants, which may be a solid at room temperature,optionally along with one or more lower viscosity lubricants, which maybe a liquid at room temperature, and optionally one or more binders,with the lower viscosity lubricant(s) having lower viscosity than thehigher viscosity lubricant(s). Exemplary higher viscosity lubricantspreferably include waxes, such as natural and synthetic waxes. Naturalwaxes include waxes derived from animal, vegetable and mineral sources,as well as mixtures thereof. In accordance with one embodiment of thepresent invention, the higher viscosity lubricant is a vegetable wax,such as carnauba wax, candelilla wax, bay berry wax, sugar cane wax andmixtures thereof.

The solid lubricant composition 40 preferably includes no more thanabout 60 weight percent of the higher viscosity lubricant, based on theweight of the solid lubricant composition (“bosc”). More specifically,the solid lubricant composition 40 preferably includes from about 30weight percent to about 60 weight percent higher viscosity lubricant,bosc. Even more specifically, in accordance with the exemplaryembodiment of the present invention, the solid lubricant composition 40includes about 55 weight percent of the higher viscosity lubricant,bosc. In alternative embodiments, the solid lubricant compositionincludes about 52 weight percent of the higher viscosity lubricant,bosc.

Suitable lower viscosity lubricants include silicones, mineral oils,polyglycols, and mixtures thereof. In accordance with the exemplaryembodiment of the present invention, the lower viscosity lubricantincludes one or more silicone lubricants. In accordance with theexemplary embodiment of the present invention, the silicone lubricant isa polysiloxane, particularly a polydimethysiloxane. One exemplarysilicone lubricant is Dow Corning 200 Fluid, commercially available fromthe Dow Corning Corporation of Midland Mich. 200 Fluid is a liquid atroom temperature.

The lower viscosity lubricant can be included in any amount providingsufficient lubricity without detrimentally impacting the cohesion of theresulting solid lubricant composition 40. Lower viscosity lubricantspreferably exhibit a lower coefficient of friction than higher viscositylubricants. However, lower viscosity lubricants can impact coatingcohesion and adhesive properties. Consequently, the solid lubricantcomposition 40 preferably includes significantly higher amounts of thehigher viscosity lubricant than the lower viscosity lubricant. Forexample, the weight ratio of the higher viscosity lubricant to lowerviscosity lubricant may be 3:2 or lower. In one embodiment, the weightratio of the higher viscosity lubricant to lower viscosity lubricant maybe 1:1 or lower, such as a ratio of about 2:3:1.

In another embodiment of the lubricant composition according to thepresent invention, the solid lubricant composition 40 preferablyincludes comparable or even lower amounts of the higher viscositylubricant than the lower viscosity lubricant. For example, the weightratio of the higher viscosity lubricant to lower viscosity lubricant maybe 3:2 or lower. This weight ratio has been found to be effective for alubricant composition comprising carnauba wax and Dow Corning 200 Fluidsilicone in 100 centistoke viscosity. Advantageously, the weight ratioof the higher viscosity lubricant to lower viscosity lubricant may be1:1 or lower, such as a ratio of about 2:3. These weight ratios havebeen found to be effective for lubricant compositions comprisingcarnauba wax and Dow Corning 200 Fluid silicone in 100 centistokeviscosity. These weight ratios have also been found to be effective forlubricant compositions comprising carnauba wax and Clearco siliconefluid in 50 centistoke viscosity. Clearco silicone fluid is availablefrom Clearco Products of Bensalem, Pa.

Accordingly, the solid lubricant composition 40 preferably includes nomore than about 60 weight percent of the lower viscosity lubricant,bosc. More specifically, the solid lubricant composition 40 preferablyincludes from about 10 weight percent to about 50 weight percent of thelower viscosity lubricant, bosc. Even more specifically, in accordancewith the exemplary embodiment of the present invention, the solidlubricant composition 40 includes about 40 weight percent of the lowerviscosity lubricant, bosc.

The lubricant composition may further comprise surfactant and heatstabilizer. Surfactant may be present in an amount of about 8 weightpercent of the surfactant, bosc. Stabilizer may be present in an amountof about 0.5 weight percent of the stabilizer, bosc.

The optional binder within the solid lubricant composition 40 may serveas an adhesive agent to provide bonding of lubricant 40 to the fabric ofthe bottom ply 26, as well as binding silicone oil into the coatingpreventing migration. Consequently, exemplary binders for use in thepresent invention include any film forming polymer known in the art thatis compatible with the remaining components within the solid lubricantcomposition 40 and provides sufficient bonding properties andflexibility. Suitable binders include polyurethanes, acrylic polymers,vinyl polymers, and the like, including mixtures and copolymers thereof.In accordance with the exemplary embodiment of the present invention,the binder is preferably polyurethane. Suitable polyurethanes includeboth polyester polyurethanes and polyether polyurethanes. In accordancewith the exemplary embodiment of the present invention, the polyurethaneis a polyester polyurethane. One suitable commercially availablepolyester polyurethane is ESTANE™. 5712 F30 polyurethane from Nonwoven,Inc. of Cleveland, Ohio.

The binder may be present in the solid lubricant composition 40 in anyamount effective to provide sufficient bonding in the bottom ply 26. Forexample, the binder may be present in the solid lubricant composition 40in an amount ranging from about 10 to 50 weight percent, bosc.Preferably, the solid lubricant composition 40 includes about 20 weightpercent to about 30 weight percent binder, bosc. More preferably, thesolid lubricant composition 40 includes from about 25 weight percent toabout 30 weight percent binder, bosc, such as an amount of about 29weight percent or about 28 weight percent.

In accordance with the exemplary embodiment of the present invention,the solid lubricant composition may optionally further include one ormore bonding agents, e.g. crosslinkers, to crosslink the binder andfurther promote cohesion within the solid lubricant composition 40 andadhesion in the bottom ply 26. Any suitable crosslinker known in the artfor use in conjunction with a given binder may be employed. Exemplarycrosslinkers include isocyantes, such as polyisocyanates anddiisocyanates, peroxides, epoxies, polyfunctional amides and mixturesthereof. In accordance with the exemplary embodiment of the presentinvention, a polyisocyanate crosslinking agent may be included in solidlubricant compositions employing a polyurethane binder.

The crosslinker is included in the composition in amounts effective toprovide a sufficient amount of crosslinking within the binder withoutimparting excessive stiffness to the resulting solid lubricantcomposition 40. Preferably, the crosslinker is present in the solidlubricant composition in amounts ranging from about 2.5 to 10 weightpercent, bosc. In accordance with the exemplary embodiment of thepresent invention, the crosslinker is preferably present in an amount ofabout 4.9 weight percent, bosc.

In accordance with the exemplary embodiment of the present invention,the solid lubricant composition 40 is formed from a liquid lubricantcomposition that is applied to, e.g. coated onto, the bottom ply 26 as aliquid lubricant composition. The solvents are then removed from theliquid lubricant composition, typically by drying and the like,resulting in a layer of the solid lubricant composition 40 substantiallycovering at least a portion of the outermost surface of, andsubstantially impregnated into, the fabric of the bottom ply 26.

The liquid lubricant composition 40 may be formed by dispersing ordissolving appropriate amounts of the higher viscosity lubricant and thelower viscosity lubricant in a lubricant solvent. The higher viscositylubricant and lower viscosity lubricant are normally incorporated intothe liquid lubricant composition in an undiluted form. The optionalbinder composition preferably contains the binder polymer dispersed ordissolved in an appropriate binder solvent. Suitable binder solventsinclude polar organic solvents, such as acetone and methyl ethyl ketone(“MEK”) and mixtures thereof. In accordance with the exemplaryembodiment of the present invention, the binder solvent is a mixture ofacetone and MEK, particularly a mixture containing about 58 partsacetone per about 42 parts MEK.

The lubricant solvent may be water, unless an isocyanate bonding agentis used. The lubricant solvent can also be any organic solvent capableof dispersing the higher and lower viscosity lubricants and bindercomposition. A suitable organic lubricant solvent is a ketone basedsolvent, such as cyclohexanone. It is understood that carnauba wax ishighly insoluble such that the carnauba wax is emulsified rather thandissolved.

The liquid lubricant composition is preferably formed by initiallycombining the higher and lower viscosity lubricants with the lubricantsolvent and heating the initial mixture to an elevated temperature, suchas a temperature of about 80° C. while the initial mixture is under lowspeed agitation. Upon dissolution of the higher viscosity lubricant, theinitial mixture may be allowed to cool to a lower, yet elevated,temperature, such as a temperature of about 55° C. Upon cooling to thelower temperature, the optional binder composition may be added, afterwhich the agitation speed may be increased and the liquid lubricantcomposition may be agitated for a period of about 5 minutes. The liquidlubricant composition is typically allowed to sit for at least 24 hours,after which the liquid lubricant composition is stirred and theviscosity is adjusted with an appropriate organic solvent, such asacetone. The viscosity of the liquid lubricant composition is preferablyabout 4000 cps (Brookfield viscosity based on a 20 rpm spindle speed).

In the embodiments of the present invention which further include acrosslinking agent, a bonding agent composition may be added to theliquid lubricant composition. The bonding agent composition preferablyincludes the crosslinker dissolved or suspended in an appropriateorganic solvent. For example, the bonding agent composition may includea polyisocyanate crosslinking agent dissolved or suspended within ethylacetate. One exemplary bonding agent composition is DESMODUR RC,commercially available from Bayer Corporation of Pittsburgh, Pa., whichcontains about 30% polyisocyanate in ethyl acetate. The bonding agentcomposition is preferably added to the liquid lubricating composition atroom temperature under high speed agitation. The resulting liquidlubricant composition is allowed to agitate at least about 3 minutesprior to use. As known in the art, the shelf life of compositionscontaining bonding agents may be limited. Accordingly, the bonding agentcomposition may be added to the liquid lubricant composition eitherimmediately prior to or a few hours before its application to the fabricof the bottom ply 26.

The liquid lubricant composition is applied to the belt material usingthe equipment and processes described above. More particularly, acoater, such as a knife coater, is used to apply the liquid lubricantcomposition to the bottom ply of the belt material and the coated beltmaterial is subsequently dried. The various solvents within the liquidlubricant composition are volatilized in the drying oven 52 (FIG. 3)following the coating process, so that the resulting solid lubricantcomposition 40 solidifies in the fabric of the bottom ply 26. The solidlubricant composition 40 is preferably at least substantially in solidform at room temperature (e.g., 72.degree. F.). The coated belt 12preferably has solid lubricant composition coat weight ranging fromabout 1 oz/sq. yd to about 5 oz/sq. yd. Most preferably, the solidlubricant composition 40 is present in the belt 12 in an amount of about72 g/m2 (2.1 oz/sq. yd).

Since the belt lubricant 40 is at least substantially solid afterdrying, migration of the lubricant 40 is substantially precluded. Also,due to the substantially solid nature of the lubricant 40, it canadvantageously be applied to rolls of belting material before sectionsare cut therefrom and spliced, because the solid lubricant does notsubstantially interfere with the splicing or adhesion. Additionally, thefabric of the bottom ply 26 may be saturated with the lubricantcomposition 40, with the lubricant composition intimately impregnated inthe fabric bottom ply, and not just on the bottom surface, so that anyloss of lubricant from the belt is insubstantial.

The depth of absorption of the lubricant composition 40 into the bottomply 26 may be controlled such that the solid lubricant composition 40 isnot dispersed throughout the thickness of the fabric of the bottom ply26. This may be accomplished during curing of the belt 12 by controllingthe temperature of the oven and the dwell time within the oven afterapplication of the liquid lubricant composition 40. Lower temperature orless dwell time will lessen the depth of absorption of the lubricantcomposition 40 into the fabric of the bottom ply 26. Another method ofcontrolling the depth of absorption of the lubricant composition intothe fabric is by controlling the solids content of the lubricantcomposition 40. Reducing the solids content of the lubricant composition40 will lessen the depth of absorption into the bottom ply 26. Inaddition, the amount of binder will affect the rheology of the lubricantcomposition 40, which effects absorption into the fabric. Specifically,increasing the amount of binder in the lubricant composition 40 willlessen the depth of absorption into the bottom ply 26.

Preferably, the binder/bonding agent in the lubricant composition 40substantially keeps the lubricant(s) on the belt 12 so thatrelubrication is not necessary. The low viscosity lubricant in thelubricant composition 40 improves lubrication, but the proportion issufficiently small so that the lubricant composition 40 is stillsubstantially solid at room temperature. Advantageously, the smallproportion of low viscosity lubricant does not substantially migrate orsubstantially interfere with belt splicing.

The endless belt, as described herein, is used in conveyor systems. Itis understood that the belt of is not limited to the type of conveyorsystem 10 illustrated and described with reference to FIG. 1, becausethe belt 12 of the present invention operates advantageously with a widerange of different types of conveyor systems, and can be used in a widerange of other applications in which belts are used. In one example, theendless belt is used in a treadmill with a waxed or unwaxed deck.

Similarly, the lubricant compositions described herein can be applied tomany different types of belts, can be used on items other than belts,and can be considered to be isolated articles of manufacture (e.g.,separate from any belts, conveyor systems, etc.) For example, it iswithin the scope of the present embodiments for the lubricant 40 to beused with (e.g. applied to and preferably impregnated into the bottomsurfaces of) conventional conveyor system belts. Likewise, the beltherein described can be used in combination with many different types oflubricants or can be considered to be isolated articles of manufacture(e.g., separate from any lubricant etc.).

Although the present invention has been shown and described inconsiderable detail with respect to a few exemplary embodiments thereof,it should be understood by those skilled in the art that we do notintend to limit the invention to the embodiments since variousmodifications, omissions and additions may be made to the disclosedembodiments without materially departing from the novel teachings andadvantages of the invention, particularly in light of the foregoingteachings. Accordingly, we intend to cover all such modifications,omission, additions and equivalents as may be included within the spiritand scope of the invention as defined by the following claims. In theclaims, means-plus-function clause(s) are intended to cover thestructures described herein as performing the recited function and notonly structural equivalents but also equivalent structures. Thus,although a nail and a screw may not be structural equivalents in that anail employs a cylindrical surface to secure wooden parts together,whereas a screw employs a helical surface, in the environment offastening wooden parts, a nail and a screw may be equivalent structures.

1. A belt assembly for use as an endless belt traveling relative to aframe structure, the belt assembly comprising: a first fabric layerhaving an inner surface and an outer surface that at least partiallyforms an upper surface of the belt, a composition comprising polyvinylchloride, the coating composition adhered to the inner surface of thefirst fabric layer such that the coating composition at least partiallyforms the inner surface of the first fabric layer; a second fabric layerhaving an inner surface and an outer surface that at least partiallyforms a bottom surface of the belt, a composition comprisingpolyurethane, the coating composition adhered to the inner surface ofthe second fabric layer such that the coating composition at leastpartially forms the inner surface of the second fabric layer; a coatingcomposition comprising polyvinyl chloride disposed between the innersurface of the first fabric layer and the inner surface of the secondfabric layer for joining the first fabric layer and the second fabriclayer; and an at least substantially solid lubricant compositionimpregnated in the second fabric layer and at least partially formingthe bottom surface of the belt.